<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>R: Root length measurements</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" type="text/css" href="R.css" />
</head><body>

<table width="100%" summary="page for secalonic"><tr><td>secalonic</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Root length measurements</h2>

<h3>Description</h3>

<p>Data stem from an experiment assessing the inhibitory effect of secalonic acids on plant growth.
</p>


<h3>Usage</h3>

<pre>data(secalonic)</pre>


<h3>Format</h3>

<p>A data frame with 7 observations on the following 2 variables:
</p>

<dl>
<dt><code>dose</code></dt><dd><p>a numeric vector containing dose values (mM)</p>
</dd>
<dt><code>rootl</code></dt><dd><p>a numeric vector containing root lengths (cm)</p>
</dd>
</dl>



<h3>Details</h3>

<p>For each dose the root length is an average three measurements.
</p>


<h3>Source</h3>

<p>Gong, X. and Zeng, R. and Luo, S. and Yong, C. and Zheng, Q. (2004) Two new 
secalonic acids from <em>Aspergillus Japonicus</em> and their allelopathic effects on higher plants,
<em>Proceedings of International Symposium on Allelopathy Research and Application, 27-29 April, 
Shanshui, Guangdong, China (Editors: R. Zeng and S. Luo)</em>, 209&ndash;217.
</p>
<p>Ritz, C (2009)
Towards a unified approach to dose-response modeling in ecotoxicology
<em>To appear in Environ Toxicol Chem</em>.
</p>


<h3>Examples</h3>

<pre>

## Fitting a four-parameter log-logistic model
secalonic.m1 &lt;- drm(rootl ~ dose, data = secalonic, fct = LL.4())
summary(secalonic.m1)

## Fitting a three-parameter log-logistic model
##  lower limit fixed at 0
secalonic.m2 &lt;- drm(rootl ~ dose, data = secalonic, fct = LL.3())
summary(secalonic.m1)

## Comparing logistic and log-logistic models
## (Figure 1 in Ritz (2009))
secalonic.LL4 &lt;- drm(rootl ~ dose, data = secalonic, fct = LL.4())
secalonic.L4 &lt;- drm(rootl ~ dose, data = secalonic, fct = L.4())

plot(secalonic.LL4, broken=TRUE, ylim=c(0,7), xlab="Dose (mM)", ylab="Root length (cm)", 
cex=1.2, cex.axis=1.2, cex.lab=1.2, lwd=2)

plot(secalonic.L4, broken=TRUE, ylim=c(0,7), add=TRUE, type="none", lty=2, lwd=2)

abline(h=coef(secalonic.L4)[3], lty=3, lwd=2)

</pre>


</body></html>
